U.S. patent number 5,673,165 [Application Number 08/516,620] was granted by the patent office on 1997-09-30 for circuit arrangement for controlling the electromagnetic drive of a switching device.
This patent grant is currently assigned to AEG Niederspannungstechnik GmbH. Invention is credited to Olaf Kuhn, Thomas Roschke.
United States Patent |
5,673,165 |
Kuhn , et al. |
September 30, 1997 |
Circuit arrangement for controlling the electromagnetic drive of a
switching device
Abstract
A reduction in contact bounce in an electromagnetic switch is
accomplished by optimizing armature speed over its travel path with
a circuit arrangement for controlling a drive current in the coil
of the electromagnetic switch. A superposed speed loop including a
speed sensor produces a measured voltage in response to speed of
the armature. A converter coupled to the speed sensor converts the
measured voltage into a value corresponding to an actual speed of
the armature. A first summer receives a constant reference value
corresponding to a desired speed for the armature and the value
corresponding to the actual speed of the armature, and produces a
difference voltage corresponding to a difference between the
desired speed and the actual speed of the armature. A proportional
element amplifies the difference voltage and produces a desired
current value corresponding to the amplified difference voltage. An
underlying current control loop including a current sensor produces
a measured current value corresponding to a current in the coil. A
second summer receiving the measured current value and the desired
current value produces an output current corresponding to a
difference between the desired current value and the measured
current value. A chopper coupled to the output current of the
second summer operates with hysteresis for conducting a pulsed
control voltage to the coil and is interrupted from doing so when
the measured current value is greater than the desired current
value plus an hysteresis value.
Inventors: |
Kuhn; Olaf (Dresden,
DE), Roschke; Thomas (Kamenz, DE) |
Assignee: |
AEG Niederspannungstechnik GmbH
(Neumuenster, DE)
|
Family
ID: |
6526987 |
Appl.
No.: |
08/516,620 |
Filed: |
August 18, 1995 |
Foreign Application Priority Data
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Aug 31, 1994 [DE] |
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44 30 867.1 |
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Current U.S.
Class: |
361/154; 361/160;
361/242 |
Current CPC
Class: |
H01F
7/1844 (20130101); H01H 47/22 (20130101) |
Current International
Class: |
H01F
7/08 (20060101); H01H 47/22 (20060101); H01F
7/18 (20060101); H01H 047/22 () |
Field of
Search: |
;361/239,242,152,154,160,170 ;307/120 ;324/420,423 ;340/644 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0376493A1 |
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Jul 1990 |
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EP |
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40 20 094 |
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Jan 1992 |
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DE |
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40 24 496 |
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Feb 1992 |
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DE |
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40 31 427 |
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Apr 1992 |
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DE |
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A-2127186 |
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Apr 1984 |
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GB |
|
Other References
Patent Abstracts of Japan, vol. 004, No. 075, May 31, 1980 &
JP-A-55 043948 (NEC Corp), Mar. 28, 1980. .
Patent Abstracts of Japan, vol. 007, No. 284, Dec. 17, 1983 &
JP-A-58 161305 (Matsushita Denki Sangyo KK) Sep. 24, 1983. .
Loffler, Dipl.-Ing. Horst, "Lineare Positionierantriebe"
Magnetmotor und Linearmotor im Vergleich, Elektronik 15/1992, pp.
48-54. .
Izadinia, Mansour et al, "H-Brucke aus einem Gu.beta."
Motor-Treiberbaustein vereinight CMOS, Bipolar und DMOS Elektronik
7/31 Mar. 1989, pp. 123-128. .
Xander, Prof. Dipl.-Ing. Karl, "Regelungstechnik mit elektronischen
Bauelementen", Werner-Ingenieur-Texte 6, Werner-Verlag, 1981, pp.
198-201..
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Primary Examiner: Fleming; Fritz
Attorney, Agent or Firm: Spencer & Frank
Claims
What is claimed is:
1. A circuit arrangement for controlling a drive current in a coil
of an electromagnetic switching device having an armature that
moves in dependence of the drive current, comprising:
a superposed speed loop including a speed sensor for producing a
measured voltage in response to speed of the armature;
a converter coupled to the speed sensor for converting the measured
voltage into a value corresponding to an actual speed of the
armature;
a first summer receiving a constant reference value corresponding
to a desired speed for the armature and the value corresponding to
the actual speed of armature, and producing a difference voltage
corresponding to a difference between the desired speed and the
actual speed of the armature;
a proportional element for amplifying the difference voltage and
producing a desired current value corresponding to the amplified
difference voltage;
an underlying current control loop including a current sensor for
producing a measured current value corresponding to a current in
the coil;
a second summer receiving the measured current value and the
desired current value and producing an output current corresponding
to a difference between the desired current value and the measured
current value; and
a chopper, operating with hysteresis, coupled to the output current
of the second summer for conducting a pulsed control voltage to the
coil, the chopper being interrupted when the measured current value
is greater than the desired current value plus an hysteresis
value.
2. The circuit arrangement as defined in claim 1, and further
comprising a free-wheeling diode connected in electrical parallel
with the coil so that the chopper is conducting current to the coil
when the measured current value is less than the desired current
value and connected in electrical series with the coil when the
chopper is interrupted so that current flows in the coil via the
free-wheeling diode.
3. The circuit arrangement as defined in claim 2, further
comprising a full-wave rectifier charged with direct or alternating
current disposed upstream of the chopper in a load circuit with the
coil.
4. The circuit arrangement as defined in claim 1, wherein the first
summer, converter and proportional element are embodied in an
operational amplifier wired as a subtracter and having a positive
input coupled to a reference voltage corresponding to the desired
speed and a negative input coupled to the measured voltage of the
speed sensor, the operational amplifier having input and feedback
resistors arranged for converting the measured voltage to the
actual speed value and for causing the operational amplifier to
amplify the difference voltage and producing the desired current
value.
5. The circuit arrangement as defined claim 1, wherein the current
sensor comprises a current-measuring resistor, the chopper
comprises a semiconductor switch, the second summer comprises a
comparator having positive and negative inputs, an output and an
adjustment resistor connected between the output and the positive
input of the comparator, the hysteresis of the chopper being
adjusted by adjustment of the adjusting resistor, the positive
input of the comparator being coupled to the desired current value,
the negative input of the comparator being coupled to the measured
current value of the current-measuring resistor, and the comparator
having a low/high output signal which is fed to the semiconductor
switch.
6. The circuit arrangement as defined in claim 5, wherein the
semiconductor switch comprises a p-channel power MOSFET.
7. The circuit arrangement as defined in claim 5, wherein the
semiconductor switch comprises an n-channel power MOSFET and a
charge pump for actuating the MOSFET.
8. The circuit arrangement as defined in claim 1, wherein the
superposed speed control loop and the underlying current control
loop are realized, in part, by algorithms in a microprocessor.
9. A circuit arrangement for controlling a drive current in a coil
of an electromagnetic switching device having an armature that
moves in dependence of the drive current, comprising:
a speed sensor coupled to the armature for producing a measured
voltage value corresponding to actual speed of the armature;
a first summer receiving a constant reference value corresponding
to a desired speed for the armature and the measured voltage value
and producing a difference voltage corresponding to a difference
between the desired speed and the actual speed of the armature;
a proportional element for amplifying the difference voltage and
producing a desired current value corresponding to the amplified
difference voltage;
a current sensor for producing a measured current value
corresponding to a current in the coil;
a second summer receiving the measured current value and the
desired current value and producing an output current corresponding
to a difference between the desired current value and the measured
current value, the output current having a first state when the
desired current value is greater than the measured current value
and a second state when the measured current is greater than the
desired current;
a chopper coupled to the output current of the second summer for
conducting said current to the coil when the output current is in
the first state and the chopper being interrupted when the output
current is in the second state.
10. The circuit arrangement as defined in claim 9, further
comprising a free-wheeling diode connected in electrical parallel
with the coil and electrical series with the chopper and being back
biased when the output current is in the first state for
controlling the chopper to conduct current to the coil, the
free-wheeling diode being connected in electrical series with the
coil and being forward biased for conducting current of the coil
when the output current is in the second state and interrupts the
chopper.
11. The circuit arrangement as defined claim 9, wherein the current
sensor comprises a current-measuring resistor connected to the
coil.
12. The circuit arrangement as defined claim 9, wherein the chopper
comprises a semiconductor switch.
13. The circuit arrangement as defined claim 9, wherein the output
current is switched to the first state when the desired current
value is greater that the measured current and is switched to the
second state when the measured current is greater than the desired
current plus a hysteresis value.
14. The circuit arrangement as defined in claim 13, wherein the
second summer comprises a comparator having positive and negative
inputs, an output and an adjustment resistor connected between the
output and the positive input of the comparator for adjusting the
hysteresis value, the positive input of the comparator being
coupled to the desired current value, the negative input of the
comparator being coupled to the measured current value of the
current-measuring resistor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority with respect to application No. P
44 30 867.1 filed in Germany on Aug. 31, 1994, the disclosure of
which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention relates to an electromagnetic switching device, such
as a contactor, solenoid, or relay, in which an armature moves in
response to a drive current in a coil and in particular to a
circuit arrangement for controlling the drive current in the coil
for reducing contact bounce of a contact member attached to the
armature.
Electromagnetic switching devices are used in automation and drive
technology, where they serve, for example, as relays which in
cooperation with other components to ensure safe control of
different electrical devices. For optimum adaptation of these
switching devices to their switching task, while taking into
consideration different operating conditions and specific device
characteristics, it can be desirable to adhere to a predetermined
speed/distance profile of the contact movement. In this way,
special switching principles can be applied so that the contact
bounce at the time of actuation can be minimized. This leads to a
reduction in burn-up and mechanical wear of the contact, which can
be translated into an increase in service life and/or maximum
switching capability of the device. The more successfully the
necessary ideal course of the speed of the switching device is
assured over the course of the contact travel, the less wear takes
place and the better the adaptation of the device to the switching
task. This type of speed/distance profile for reducing bounce can
essentially be attributed an optimum speed during the making of
contact and a reduction in speed when the core halves impact. This
optimum speed during the making of contact is usually smaller than
the speed of the uncontrolled switching device, which varies in a
wide range. The increase of the contact travel up to the making of
contact due to burn-up is a particular hindrance, because the ideal
course of the speed/distance characteristic curve is consequently
changed over the service life of the switching device.
A reduction in bounce can partially be accomplished by a better
matchup between the contact, transmission and drive systems of the
switching device. This matchup is only possible for certain
conditions, mostly nominal or rated operating conditions, but not
for the whole range of allowed conditions. In contrast, maintaining
a certain speed/distance profile assures a reduction of bounce
under all acceptable conditions of use over the entire service life
of the switching device, with the consideration of the
manufacturing tolerances of the device. The effective maintenance
of this ideal curve can be realized by circuit arrangements that
are suitable for controlling the course of movement.
European patent application No. EP 0 376 493 A1 discloses a control
circuit with which the movement process of electromagnetic relays
is influenced in order to reduce the incidence of bounce. In this
case, a very high current is permitted in the first phase of
movement for the purpose of rapid acceleration. Before the relay is
closed, the current is reduced to a relatively small value, and the
speed of movement of the armature/contact correspondingly assumes a
smaller value, which leads to reduced bouncing.
The objective of the known circuit arrangements for electronic
switching drives is to reduce armature speed, without a special
contact-making speed optimized to minimum bounce being achieved at
the same time. Further, only fluctuations in the control voltage
and, to a certain extent, the temperature, are compensated or taken
into consideration. Likewise, disturbances of desired armature
motion such as burn-up, friction and tolerances are not
considered.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a circuit
arrangement for controlling the drive of an electromagnetic
switching device, by means of which the maintenance of optimum
contact-making speeds and the limitation of the armature core
impact speed are assured, with the simplest means, over the entire
service life of the switching device, and in spite of disturbances
caused by burn-up, friction and tolerance the permissible ranges
for control voltage and temperature are even expanded, and greater
tolerances can be permitted.
The above and other objects are accomplished according to the
invention by the provision of a circuit arrangement for controlling
a drive current in a coil of an electromagnetic switching device
having an armature that moves in dependence of the drive current,
including: a superposed speed loop including a speed sensor for
producing a measured voltage in response to speed of the armature;
a converter coupled to the speed sensor for converting the measured
voltage into a value corresponding to an actual speed of the
armature; a first summer receiving a constant reference value
corresponding to a desired speed for the armature and the value
corresponding to the actual speed of armature, and producing a
difference voltage corresponding to a difference between the actual
speed and the desired speed of the armature; a proportional element
for amplifying the difference voltage and producing a desired
current value corresponding to the amplified difference voltage; an
underlying current control loop including a current sensor for
producing a measured current value corresponding to an actual
current in the coil; a second summer receiving the measured current
value and the desired current value and producing an output current
corresponding to a difference between the desired current value and
the measured current value; and a chopper, operating with
hysteresis, coupled to the output current of the second summer for
conducting a pulsed control voltage to the coil when the measured
current value is greater than the desired current value plus an
hysteresis value.
The circuit arrangement of the invention can be used in
electromagnetic switching devices that are operated both with
direct and alternating current. Furthermore, their effectiveness is
independent of the turn-on phase position of the control voltage,
and the switching process begins without delay initiated by a
control circuit, so the closing delay time is scarcely increased
compared to a non-controlled switching device.
The circuit arrangement is distinguished by a simple design, which
does not require a memory for desired curves or a microcontroller
for controlling the drive. The use of a simple speed sensor also
permits suppression of the influence of disturbances such as
fluctuations of control voltage, burn-up of the contacts,
temperature, friction and/or assembly and manufacturing tolerances,
within a wide range.
Further advantageous embodiments and features of the invention will
become apparent from the following detailed description and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a circuit arrangement according to the
invention for controlling the drive current, and thus the armature
speed, of an electromagnetic switching device.
FIG. 2 is a circuit schematic for implementing the arrangement of
FIG. 1.
FIGS. 3a-3c are diagrams showing control voltage, speed and current
curves, respectively, for explaining operation of the
invention.
FIG. 4 is a diagram which shows speed curves under different
operating conditions.
FIG. 5 is a block diagram for implementing the arrangement of FIG.
1 using a microprocessor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown a block diagram of a circuit
arrangement for controlling the movement of an armature 1 in an
electromagnetic switching device, not shown in detail, particularly
in a contactor, solenoid, or relay having a coil 3, which is
connected to a chopper 19 for generating pulsed control voltages. A
superposed speed loop is provided which includes a speed sensor 7
that measures the speed of armature 1 and supplies a measuring
voltage V.sub.m proportional to speed to a converter 9. Speed
sensor 7 can have a variety of configurations, for example, it can
be inductive or optical, as will be appreciated by those skilled in
the art. The measurement voltage from sensor 7 is converted in
converter 9 into voltage a V.sub.a value that corresponds to actual
speed of the armature, and is fed to a summing device 11 for
determining a difference between the actual armature speed V.sub.a
and a desired speed value v.sub.d fed to the positive input of
summing device 11 as a constant reference value.
This desired speed value v.sub.d is a desired value that remains
constant during the entire control process. Its value corresponds
approximately to the desired armature speed at a time that contact
is made.
An output signal from summing device 11 that corresponds to a
difference voltage .DELTA.v is then conducted to a proportional
element 13 for conversion and amplification in order to form a
desired current value I.sub.d. The signals of the desired current
value I.sub.d and a measured current value I.sub.m in coil 3 are
fed to a summing device 15, in which the difference current
.DELTA.I between the desired current value I.sub.d and the measured
current value I.sub.m is determined. The measured current value
I.sub.m results from the measured voltage determined, for example,
by means of a measuring resistor 17.
With a positive current control deviation .DELTA.I=I.sub.d
-I.sub.m, i.e., the desired value of the current is greater than
the measured current value, chopper 19 is closed and a rectified
supply voltage is conducted from a full-wave rectifier 18 to coil
3.
With a negative control deviation .DELTA.I, the operation of
chopper 19 is interrupted, and the coil current then flows via the
measuring resistor 17 and a free-wheeling circuit having a
free-wheeling diode 21 as better illustrated in FIG. 2 discussed
below. Thus, the current in the coil 3 is maintained up to the next
turn-on pulse of the chopper 19. The full-wave rectifier 18 can be
charged with direct or alternating current.
In an advantageous embodiment, chopper 19 operates with hysteresis.
For this purpose, chopper 19 does not interrupt the circuit until
the measured current value I.sub.m lies above a desired value by a
fixed hysteresis value I.sub.Hysteresis. The underlying current
control loop can be used in connection with chopper 19 operating
with hysteresis for holding pulses after the pick-up process in
that a fixed holding current limiting value is fed to the summing
device 15. Switching from derived current value I.sub.d to such a
constant holding current is advantageously carried out by means of
a constant time element for the change-over-time whose time
constant is clearly greater than the maximum possible total closing
time.
In accordance with the invention, a superposed speed-control loop
and a dynamically faster, underlying current-control loop form a
circuit arrangement for an electro-magnetic switching device, with
which a reduction in contact bounce and thus a reduction in burn-up
is accomplished by an optimum contact-making speed and a limited
armature core impact speed. This lengthens the service life of the
switching device and/or increases switching capability, while the
speeds under the influence of fluctuations in control voltage,
permissible ambient temperatures, tolerances, contact burn-up and
friction are held relatively constant for the duration of use.
FIG. 2 shows a circuit schematic for implementing the block diagram
in FIG. 1. A subtracter 23 is provided that forms a difference
between the desired speed value V.sub.d and the actual speed value
V.sub.a resulting from the measured speed V.sub.m measured with
speed sensor 7 according to FIG. 1. The desired speed value is
proportional to a reference voltage value V.sub.Ref which remains
constant. The speed difference is amplified in an operational
amplifier 12 by the resistance ratio R.sub.N /R.sub.V of resistors
25, 27, 29, 31, so that the desired value U.sub.i-des for the
current is present at the output of subtracter 23. A possibly
necessary calibration factor of the speed sensor can also be
considered in the amplification of subtracter 23. The desired value
of the current is fed to a comparator 16 as a reference or
threshold value. As long as the measured value of the current
U.sub.i-means is less than the reference value, a high potential is
present at the output of comparator 16. An n-channel power MOSFET
39 is controlled by a charge pump 37 for conducting current from
full-bridge rectifier 18 to coil 3. As soon as the measured value
U.sub.i-mess becomes greater than the reference value U.sub.i-des
plus a switching hysteresis that can be adjusted by means of a
resistor 33 connected in parallel by way of the comparator 16, a
low potential is present at the output of the comparator 16, and
the semiconductor switch 20 is blocked. The current of the coil 3
then flows via the free-wheeling diode 21. The semiconductor switch
20 can also comprise a p-channel power MOSFET.
FIGS. 3a-3c illustrate a pick-up process controlled in accordance
with the invention, in which the time units are the same in each
figure. FIG. 3a shows the temporal course of the pulsed control
voltage, wherein the control voltage is a rectified AC voltage
which is controllably interrupted by semiconductor switch 20 in
accordance with the invention. FIG. 3b shows the constant desired
value for speed and the actual value for speed during the pick-up
process. The times at which contact is made and of impact of
armature cores, as the core halves are closed, are shown. The
desired and measured values for the current are illustrated in FIG.
3c. The desired value of the current results from the difference
between the desired and actual speed, which can be seen in FIG. 3b,
and is amplified by a factor K. Only when the speed of the armature
approximates its desired value, and the speed difference is thus
small enough, is the control supply voltage shut off by the chopper
19. Up to this point, the available energy is consumed completely
in order to accelerate the armature. Consequently, an advantage of
the circuit arrangement of the invention is the shortest possible
pick-up times and, as a function of the switching hysteresis, only
a few switching cycles. This low switching frequency leads to good
EMC (Electromagnetic Compatibility) properties and a lower stress
on the semiconductor components.
FIG. 4 illustrates three speed curves of the armature under special
conditions. The dashed line 3 shows the worst case at maximum
excess energy, where the highest control voltage, the lowest
temperature, the least friction, the least load spring force and
the smallest air gap during the making of contact at maximum
burn-up are present. The opposite extreme case, at minimum energy
for pick-up, is represented by the solid line 1. The speed curve
under normal conditions (when the device is new and operating under
nominal conditions) is represented by the dotted line 2. The more
excess energy that is available, the sooner the pick-up process is
completed. The speeds, particularly at the time contact is made,
deviate only slightly from one another because of the circuit
arrangement according to the invention.
In a modification of the foregoing, the superposed speed control
loop and the underlying current control loop may be realized, in
part, by algorithms in a microprocessor.
FIG. 5 shows a microprocessor 43 with at least two
analog-digital-converters for measured speed V.sub.measure and
measured current I.sub.measure. The current through the coil is
measured by a contactless current transducer 17. The function of
the superposed speed-control-loop and the underlying
current-control-loop are converted into algorithms. A digital
output of the microprocessor charges an optocoupler 41 which
controls the semiconductor switch. This switch is for example
carried out as an charge pump 37 and a n-channel power MOSFET
39.
The invention has been described in detail with respect to
preferred embodiments, and it will now be apparent from the
foregoing to those skilled in the art that changes and
modifications may be made without departing from the invention in
its broader aspects, and the invention, therefore, as defined in
the appended claims is intended to cover all such changes and
modifications as fall within the true spirit of the invention.
* * * * *